Modern lighting device, and in particular LED-based lighting devices, show long lifetimes, even up to 40,000 hours are claimed. Due to their long lifetime, these types of lamps constitute an extensive and worldwide market today.
One of the most widely used halogen lamps, the standard halogen MR 16 spots, are today to a large extent replaced by “retrofit” LED based lamps, often referred to as retrofit LED MR 16 lamps. Since there is a maximum tolerated temperature within the lamp, thermal constraints will limit the available light output. That is to say, the more heat generated within the lamp, the better heat spreading from the lamp will be required.
In many applications, the MR 16 spot is encapsulated by glass, and the only contact with the ambient is via the front exit window. Glass is often chosen in these types of LED lamps as it is a cheap and sustainable basic material. There are several advantageous properties of glass such as low cost, sustainability, suitable optical properties, and electrical insulation function. However, a drawback of glass is its thermal properties. The thermal conductivity of glass is about 1 W/(m·K). The thermal conductivity of glass encasing is better than plastics but worse than e.g. metal casing like aluminum. As a result, the heat dissipation from a glass encapsulated MR 16 lamp is relatively poor, and will negatively impact the performance of the LEDs.
An improved thermal performance can be realized by using active cooling, e.g. a fan. However, such a solution as well as other active cooling techniques available on the market today is rather complicated and expensive.